The present technology relates to an optical disc apparatus for recording/reproduction on/from an optical disc recording medium, a tilt correction method for the optical disc apparatus, and a program for running in the optical disc apparatus.
Optical disc recording media (hereinafter, referred to also as optical discs) have been widely available, e.g., CDs (Compact Discs), DVDs (Digital Versatile Discs), and BDs (Blu-ray Discs™)
Such optical discs are subjected to recording and reproduction by an optical disc apparatuses, which is sometimes provided with a function of tilt correction. With the tilt correction function, angular deviation (tilt) of laser light from the optical axis entering the recording surface of an optical disc is corrected. This is to prevent the servo and recording/reproduction performances from being impaired by coma aberration to be caused by the tilt.
Such tilt occurs mainly due to warping of the optical discs, i.e., disc tilt. The optical disc apparatus corrects such disc tilt generally by tilting an objective lens, i.e., by tilting the optical axis of the objective lens through which laser light passes.
For such tilt correction, the objective lens is actually tilted differently for signal detection at a plurality of tilt positions, and based on the results thereof, a correction value considered optimal (tilt adjustment value) is found, i.e., a search is made for an optimal tilt adjustment value.
In other words, by using the search result of an optimal tilt adjustment value found as such as a basis for tilt correction, the tilt correction is made appropriately to the combination of an optical pickup and an optical disc actually in use.
With such tilt correction, if with a ROM (Read-Only Memory) disc specifically for reproduction use, for example, an estimation value based on a reproduced signal may be used as an estimation indicator during the search for the optimal tilt adjustment value as above.
However, if with a recordable disc, e.g., a not-yet-recorded disc (blank disc) or a partially-recorded disc, such an estimation indicator based on the reproduced signal may not be used during the search.
Therefore, for the search for an optimal tilt adjustment value when a recordable disc is in use, the estimation indicator for use is the amplitude of a push-pull signal or that of a tracking error signal (for example, see Japanese Patent Application Laid-open No. 2004-234783 (hereinafter, referred to as Patent Document 1)).
The issue here is that, in comparison with a case of using the estimation indicator based on the reproduced signal, when the estimation indicator in use is the amplitude of the push-pull signal or that of the tracking error signal, the accuracy of the search for the optimal tilt adjustment value seems to be reduced.
In consideration thereof, Patent Document 1 referred above describes the technique for improving the accuracy of the search for a tilt adjustment value using the amplitude of a push-pull signal or that of a tracking error signal.
To be specific, in Patent Document 1, two types of search are made for an optimal tilt adjustment value; one is with an estimation value based on a reproduced signal using any recorded section, and the other is with the amplitude of a push-pull signal. The results of such searches are tilt correction values (S1 and S2), and a difference therebetween (ΔS) is calculated beforehand. Thereafter, a search for an optimal tilt adjustment value using the amplitude of the push-pull signal is made again this time at a recording-start position (not-yet-recorded region). The resulting tilt adjustment value (S3) is revised using the difference, and based on the resulting tilt adjustment value revised as such, tilt correction is performed.